One conventional ion beam generator is disclosed in patent publication 2005-506656A. When the ion beam generator is used in a sputtering or etching system, an appropriate gas such as argon is introduced into a discharge chamber through gas introducing means. A plasma is generated by applying a rf power to the gas. Normally, the generated plasma is confined within the discharge chamber. Part of the plasma is in the vicinity of ion beam extraction units in respective facets. An assembly of grids which extract ions from the discharge chamber thereinto and accelerate ions therethrough are provided in each of the ion beam extraction units.